Wechsler Intelligence Scale for Children (WISC)

The Wechsler Intelligence Scale for Children (WISC) has been around since 1949 as an adaptation of David Wechsler’s 1939 Wechsler-Bellevue Intelligence Scale. This version of the Wechsler test is a psychological assessment that measures different aspects of intelligence and is designed for children between the ages of 6 to 16. The test has undergone several updates and the current version of the test is the fifth edition WISC-V which was released in 2014.

Though this test can be used as an IQ test for children, it is most often used as a clinical tool to measure individual cognitive abilities. The WISC is often used among a battery of other tests to assess and identify cognitive function and ability ranges which can help identify giftedness, learning disabilities, or general strengths and weaknesses a child may have in their cognitive abilities. Learning disabilities can be identified by comparing results from an intelligence test like the WISC with the scores from an achievement test like the Wechsler Individual Achievement Test to identify gaps between academic achievement and a child’s level of intellectual functioning.

The developers of this intelligence test recognize that a child’s performance must be compared to individuals similar to them, and each version of the WISC uses normative samples to compare a child’s score to. Age has the most significant effect on how a child performs on a certain task. Therefore, raw scores of each subtest are calculated and then compared to the normative sample with children of the same age.

This test relies on the idea that cognitive skills, or intelligence, are normally distributed throughout the population. Normal distribution means that most people fall within the average range and less people perform at a range that is above or below average.

Wechsler Intelligence Scale for Children Scoring Explained

Scores for this test are determined based on statistical values such as the mean (the average) and standard deviation (a calculation that determines a significant distance of a score from the average). Once a child’s performance on a subtest is compared to the normative sample, subtest scores are converted into scaled scores that serve as one of the universal metrics for this test.

A scaled score of 10 is the mean and scaled scores that deviate 3 units reflect a standard deviation. Similar subtests are then combined into Primary Index Scales that have a mean of 100 and standard deviation of 15. These numbers help determine the classification for performance.

Classification of performance for scaled index scores are as follows:

Below Average – scaled score 1 to 5

Low Average – scaled score 6 to 7

Average – scaled score 8 to 11

High Average – scaled score 12 to 13

Superior – 14 to 15

Very Superior – 16 to 20

Descriptors of performance for standard WISC score ranges are as follows:

Below Average – standard score below 79

Low Average – standard score 80 to 89

Average – 90 to 109

High Average – 110 to 119

Superior – 120 to 129

Very Superior – above 130

Clinicians use this test for many different reasons and may report all or only some scores. Nevertheless, the following will cover the standard measures offered by the WISC-V, the most recent version of this assessment. It should be noted that there are a number of other analyses beyond the scope of this writing that clinicians may report.

How the WISC is Administered

The fifth version of this test is done individually with the child and clinician and can be done in standard paper-and-pencil administration or on a tablet, digital format. This test includes a total of 16 subtests; however, the standard number of subtests given is 7. Raw scores on these subtests are converted into scaled scores and then the sum of scaled scores of similar tests is converted into a Primary Index Scale.

WISC Index Scores

There are a total of five Primary Index Scores that make up the Full Scale IQ score: Verbal Comprehension, Visual Spatial, Fluid Reasoning, Working Memory, and Processing Speed. The Verbal Comprehension Index reflects the ability to access and apply word knowledge. The core subtests include Similarities (how to words are similar) and Vocabulary.

The Visual Spatial Index reflects the ability to understand visual details and relationships in order to solve puzzles and construct geometric designs. The core subtests are Block Design (orienting blocks to match a picture) and Visual Puzzles (visual spatial integration).

The Working Memory Index reflects the ability to register, maintain, and manipulate visual and auditory information. The core subtests are Digit Span (repeating number sequences) and Picture Span (auditory and visual attention and working memory, respectively).

The Processing Speed Index reflects the speed at which a child can accurately make decisions. The core subtests are Coding (matching symbols to associated numbers) and Symbol Search (visual scanning and graphomotor speed of matching symbols).

Verbal Comprehension Index measures a child’s ability to verbally reason, which can be heavily influenced by their semantic knowledge. This index score is derived from the Similarities, Vocabulary, Information, and Comprehension subtests.

Scores on the five Primary Index Scales are then combined and converted into a Full Scale Intelligence Quotient (FSIQ), which is designed to measure overall intelligence.

History of the Wechsler Intelligence Scale for Children

As mentioned previously, the WISC has undergone several revisions. With each successive rendition of the test, the scoring of the test had to account for the Flynn effect to properly scale scores. The Flynn effect is the recognized improvement in human beings’ fluid and crystallized intelligence during the 20th century. So, for example, a child with an average score of 100 in 2018 is actually representative of a higher level of intelligence than a child who scored a 100 in 1968.

The initial WISC test was launched in 1949 and was next updated with the WISC-R in 1974. The WISC-R featured the same subtests, but updated the age range for the children it tested from a range of 5-15 to 6-16. The WISC-III was published in 1991 and added a subtest for processing speed. The WISC-III also introduced new index scores to represent specific areas of intelligence, (which have since been updated):

Verbal Comprehension Index

Perceptual Organization Index

Freedom of Distractibility Index

Processing Speed Index

The WISC-IV arrived in 2003 and was fairly quickly followed by the WISC-V in 2014.

Reliability of the Wechsler Intelligence Scale for Children

This test is the gold standard for intellectual assessment for children, partly because of its reliability. Reliability is important because it ensures that test-takers will achieve similar scores each time they take the test. Several studies have measured the reliability of the fifth edition of this test with strong findings, suggesting that the scores a child receives on the subtests and index scales of this test are reliable measurements.